The present invention relates to a joint-pipe for a carburetor mounted in a 2-cycle internal combustion engine in which a reed-valve is provided at the suction port formed in a crank case to permit a pre-compression of air-fuel mixture.
In some of 2-cycle internal combustion engines having a small displacement used in portable chain saw or the like apparatus, a reed valve is mounted in a mixture suction port provided in the wall of crank case, in order to permit a pre-compression of the mixture. In such internal combustion engines, it is often experienced that the engine operation is unsmoothed particularly in an extremely low engine speed as in the case of starting up, due to insufficient opening of the reed valve. It is well known to use, in 2-cycle internal combustion engines of the type described, a diaphragm type carburetor for reducing the size. In such carburetor, it is not possible to sufficiently mix the air and fuel with each other, and the fuel undesirably attach to the surface of the wall defining the mixture intake passage to form a liquid film of fuel which flows down along and in contact with the wall surface. This imposes a problem particularly when the carburetor is disposed at an offset to the suction port due to a reason concerning the construction. Namely, in such a case, the intake mixture passage is inevitably bent so that the liquid fuel tends to attach heavily to the outer part of curvature of the bent passage to unsmooth the engine operation.
In some engines of the kind described, two cylinders are arranged horizontally to oppose to each other in such a manner as to make a common use of the crank case and ignition takes place in both cylinders simultaneously so as to reduce the vibration generated in the engine. In such a type of engine, it is essential that a sufficiently mixed air-fuel mixture is sucked towards the center of the crank case, in order to equalized the operating conditions of two cylinders.